Switching power converters utilizing coupled inductors are known. In particular, U.S. Pat. No. 6,362,986 to Schultz et al., which is incorporated herein by reference, discloses, among other things, DC-to-DC converters including coupled inductors. These DC-to-DC converters typically have a higher effective switching frequency and a lower steady state peak-to-peak ripple magnitude than corresponding DC-to-DC converters utilizing discrete (uncoupled) inductors.
Coupled inductors that may be used in switching power converters have been proposed. For example, coupled inductors are disclosed in U.S. Patent Application Publication Number 2009/0237197 to Ikriannikov et al., which is incorporated herein by reference. FIG. 1 shows a perspective view and FIG. 2 shows a top plan view of a coupled inductor 100, which is similar to some of the coupled inductors featured in Publication Number 2009/0237197. FIG. 3 shows a top plan view of coupled inductor 100 with windings 102 omitted to show underlying features more clearly, and FIG. 4 shows a perspective view of one winding 102. In FIG. 2, windings 102 are represented by dashed lines where obscured by end magnetic elements 104, 106 in the top plan view.
Coupled inductor 100 includes a magnetic core 103 including first and second end magnetic elements 104, 106 and four connecting magnetic elements 108 (see FIG. 3). A respective winding 102 is wound around each connecting magnetic element 108. Each winding has a respective first end 110 extending under first end magnetic element 104, and each winding has a respective second end 112 extending under second end magnetic element 106 (see FIG. 2). In this disclosure, specific instances of an item may be referred to by use of a numeral in parentheses (e.g., winding 102(1)) while numerals without parentheses refer to any such item (e.g., windings 102).
As taught in U.S. Pat. No. 6,362,986, a switching power converter utilizing a coupled inductor must be configured to achieve proper magnetic coupling between the windings, to realize the benefits associated with using a coupled inductor. Specifically, the switching power converter must be configured as follows to achieve such proper magnetic coupling between the windings: (1) magnetic flux generated by the windings constructively interferes when one winding is switched to an excitation voltage (e.g., an input voltage) and the remaining windings are switched to a control voltage (e.g., ground), and (2) magnetic flux generated by the windings effective collides when all of the windings are switched to either the excitation voltage or to the control voltage. Accordingly, proper magnetic coupling requires a suitable coupled inductor, as well as proper excitation of the inductor by the switching power converter.
For example, FIG. 5 is a schematic of a four-phase buck converter 500 that achieves proper magnetic coupling between windings utilizing coupled inductor 100. A first end 110 of each winding 102 is electrically coupled to a respective switching node 502. Each switching node 502 is electrically coupled to an input power source 504 via a respective switching device 506, as well as to a control voltage rail 508 (e.g., ground) via a respective diode 510. Each pair of switching device 506 and diode 510 electrically coupled to a common switching node 502 is sometimes referred to as a switching stage 512. A second end 112 of each winding 102, as well as a filter 514, are electrically coupled to an output node 516.
A controller 518 monitors output node 516 via a feedback line 520 and causes switching devices 506 to repeatedly switch between their conductive and non-conductive states via control lines or a control bus (not shown) to regulate voltage on output node 516 and/or current delivered to a load (not shown) from output node 516. Controller 518 switches each switching device 506 out of phase (e.g., 90 degrees out of phase) with respect to each other switching device 506. Diodes 510 provide a path for current flowing through windings 102 when switching devices 506 turn off.
The configuration of coupled inductor 100 requires that either (1) all of its winding's first ends 110 are electrically coupled to respective switching nodes 502 (as shown in FIG. 5), or (2) all its winding's second ends 112 are electrically coupled to respective switching nodes 502, to achieve proper magnetic coupling in buck converter 500. As known in the art, electrical connections between switching stages 512 and windings 102 need to be short to prevent excessive resistive losses and parasitic ringing at the connections. Typical configurations of coupled inductor 100 dictate that all switching stages 512 be disposed on a common side of coupled inductor 100 to be near either first ends 112 or second ends 112 of windings 102.
For example, FIG. 6 shows a printed circuit board (PCB) layout 600, which is one possible PCB layout of buck converter 500 that achieves proper magnetic coupling with coupled inductor 100. Rectangle 602 represents the outline of coupled inductor 100. Each first end 110 of each winding 102 electrically couples to a respective switching node pad 604, which is in turn electrically coupled to a respective switching stage 512 via a respective circuit trace 606. Each second end 112 is electrically coupled to a respective output pad 608, which forms part of output node 516. Switching stages 512 are disposed on a common side 610 of coupled inductor 100 to be near the first ends 110 of their respective windings 102. Switching stages 512 have a pitch 612 with spacing 614 between adjacent switching stages.